1. Field of the Invention
The present invention relates to a lithography system and a lithography method.
2. Description of the Related Art
As the demand for microfabrication of semiconductor devices increases, not only a conventional photolithography technology but also a microfabrication technology in which a mold and an uncured resin on a substrate are pressed against each other to thereby form a resin pattern, which corresponds to the fine concave and convex pattern formed on the mold, on the substrate have received considerable attention. This technology is also referred to as an “imprint technology”, by which a fine structure with dimensions of a few nanometers can be formed on the substrate. One example of imprint technologies includes a photo-curing method. An imprint apparatus employing the photo-curing method first applies an ultraviolet curable resin (imprint resin, photocurable resin) to the shot area (imprint area) on the substrate (wafer). Next, the resin (uncured resin) and a mold are pressed against each other. After the ultraviolet curable resin is irradiated with ultraviolet light for curing, the cured resin is released from the mold, whereby a resin pattern is formed on the substrate.
Also, in the imprint apparatus, the transfer accuracy needs to be in the order of a few nanometers as described above while keeping the positioning error tolerance caused by the apparatus in the range of from a few to tens of nanometers and the transfer speed also needs to be increased. In general, the transfer speed using an imprint apparatus takes a longer time as compared to using an exposure system such as a conventional stepper, scanner, or the like, and thus, the throughput of a single imprint apparatus is low. Accordingly, for example, a method for driving a substrate stage, which effects positioning of a substrate, at high speed, or a method for employing an imprint system having a cluster configuration in which a plurality of imprint apparatuses is installed at a device manufacturing factory may be employed. In particular, when an imprint system having a cluster configuration is used, the cost for each imprint apparatus is lower as compared to that for each liquid immersion exposure apparatus. Consequently, such an imprint system is advantageous in achieving low cost even when a plurality of imprint apparatuses is installed.
However, an improvement in transfer speed and transfer accuracy may often be in a tradeoff relationship. Specifically, a high speed drive of a substrate stage may not only increase a reaction force, which is generated therein, to thereby vibrate the apparatus but also affect other apparatuses that are disposed therearound. In particular, even if the vibration generated in a single apparatus is small in the case of employing a cluster configuration, the vibration is amplified by superimposing a phase and a directional component of vibration generated in a plurality of apparatuses, resulting in vibration of the entire floor of a factory having a cluster configuration. For example, in an imprint apparatus, when a mold is pressed against a photocurable resin to each other during an imprint operation, a positional relationship therebetween is held with high accuracy depending on the pre-acquired positional condition. However, when such vibration is delivered to the apparatus, the contact interface between the mold and the uncured resin becomes unstable, resulting in degradation in transfer accuracy. Hence, in the case of a high-value-added exposure apparatus, for example, a counter mass is installed to eliminate vibration to be delivered to the exterior. Consequently, the effects on surrounding other exposure apparatuses therearound are reduced. In contrast, the installation of a counter mass is disadvantageous for an imprint apparatus that is advantageous in reducing cost or footprint. Therefore, in an imprint apparatus, a vibration isolation unit, which is provided as an alternative to a counter mass, is typically installed so as to block transmission of vibration from the exterior as much as possible.
An example of such a vibration isolation unit includes a so-called active-type vibration isolation unit that detects vibration of an object to be vibration-isolated and vibration of a floor on which the apparatus is located using a measuring instrument, and drives the object to be vibration-isolated using an actuator depending on an output signal. The active-type vibration isolation unit has a vibration isolation performance higher than that of a passive vibration isolation unit configured only by a support mechanism having spring and damper characteristics. In this case, there are two methods for controlling the drive of an actuator. One of the methods is a controlling method (feedback control) for directly detecting vibration of an object to be vibration-isolated using a measuring instrument and driving an actuator so as to suppress such vibration. The other method is a method (feedforward control) for providing a measuring instrument for measuring the vibration of the installation floor and predicting the vibration to be delivered from the installation floor to the object to be vibration-isolated depending on the output value by the measuring instrument to thereby drive an actuator so as to cancel out such vibration. The former method has its limits for the complete control since control is executed in a reflective manner based on disturbances generated in the object to be vibration-isolated. However, the latter method has a great effect of isolating vibration since control is executed in advance with respect to such disturbance. The vibration isolation unit disclosed in Japanese Patent Laid-Open No. 2001-20996 employs a control technology as described above. On the other hand, the active vibration isolation unit disclosed in Japanese Patent Laid-Open No. 2008-115966 executes feedforward control not based on measurement information from the installation floor but based on the drive signal of a moving body on the object to be vibration-isolated.
However, since the vibration isolation unit disclosed in Japanese Patent Laid-Open No. 2001-20996 measures the vibration of the installation floor and executes feedforward control based on the measured value, the control result may readily be influenced by the capability of the measuring instrument. In other words, the vibration isolation unit generates the driving force of an actuator based on the measured value. Thus, if an error exists in the measured value, the vibration isolation unit may undesirably amplify the vibration. Also, in a typical measuring instrument, noise is readily superimposed upon measuring vibration in a low frequency range, and thus, a high pass filter or the like may be used so as to eliminate effect of such noise. Furthermore, a low eigenvalue member is used in the vibration isolation unit so as to ensure the vibration isolation performance. However, since the vibration isolation unit resonates in a low frequency range, the vibration isolation unit needs to suitably suppress vibration having a low frequency component. For that purpose, since the measured value components in a low frequency range is eliminated in the vibration isolation unit, the effective vibration isolation effect may not be obtained.
Also, in the active vibration isolation unit disclosed in Japanese Patent Laid-Open No. 2008-115966, the position and the acceleration of a moving body are estimated based on control information for the moving body, and a control force is directed to an actuator further based on these values. In this case, since a moving body is present on an object to be vibration-isolated, a force to be imparted to the object to be vibration-isolated by the moving body is readily estimated. However, the active vibration isolation unit has no effect on the vibration from the installation floor.